Most grouse in Maine are road or tree-wrenched. Spend time walking the unpaved woods roads and rail beds and note the 3" .410 empties. Lots of them.

Not just that - they're mostly stamped #6 or #4. There's a reason: put such loads on paper at 40 yds using a "full" stamped 42, 37....or any of a slew of other single shot hammerguns.